1. Field of the Invention
The present invention relates generally to a cylinder lock of the type that uses a keyway adapted to receive a specially milled key blank that is bitted to fit a particular lock. More specifically, this invention relates to rebroaching a previously broached twisting tumbler cylinder lock comprising a cylinder plug having a given longitudinal axis and rotatable within a cylinder shell about said longitudinal axis under the control of a plurality of twisting tumblers. Such locks are constructed and arranged to have a large number of possible pin tumbler combinations of angles, positions and depths.
2. State of the Prior Art
In the past, the assignee of various patents covering lock devices maintained a security list of the construction and arrangement of the components of each lock of this type and included with this list the location of the particular lock so that in case a key capable of opening the lock in question was lost, a new security bitting could be provided without causing the owner of the key to lose his security.
Each of the twisting tumblers of a preexisting lock of the prior art locks to be modified to provide a novel lock assembly of this invention is provided with a bottom pin having key-contactable surface means, provided by a key contacting point at each tumbler position. Each key contacting point is oriented at any one of three different angles and is located at any one of several different depths. Each of the tumblers comprises a preexisting set of tumbler components comprising a spring, a top pin or driver, and an aforesaid bottom pin. A removable cover holds an associated set within a separate cylindrical pin chamber associated with each tumbler set corresponding thereto. Each of the bottom pins has a flag that extends radially outward from its upper portion through an axial slot in the peripheral wall of the corresponding cylindrical pin chamber. The flag extends through the axial slot to orient its associated tumbler in a given radial plane common to corresponding axial slots of remaining pin chambers spaced along the longitudinal axis of the cylinder plug.
The construction just described provides a broach for each cylindrical pin chamber. The broaches for the cylindrical pin chambers are oriented in a common radial plane extending through the given longitudinal axis. In this manner, an owner of a series of patents on various locks of the type described generally could control an inventory of key bittings sold to different customers and provide any customer with a substitute key whenever an original key provided to open any lock in the inventory of locks maintained by the patent owner was lost. However, after certain of the patents controlling these locks expired, it became a misuse of patents for a patentee to continue to control the sale of unpatentable keys for opening locks covered by the expired patents. It became a matter of public interest for one skilled in the art of lock making to develop a technique whereby a preexisting lock no longer protected by a patent could be used in a combination with a key of different milling without extending the effective period of patent protection for the lock.
The following patents of which the inventor is aware represent the state of the prior art to the best of the knowledge of the inventor.
U.S. Pat. No. 685,772, issued Nov. 5, 1901 to Lapointe, shows a key seat cutter that reciprocates to modify preexisting grooves, key-seats or splines in the inner faces of hubs, collars, sleeves and the like, but is not capable of creating a new broach at a fixed angle to a preexisting broach.
U.S. Pat. No. 2,510,835 to Rice, issued Jun. 6, 1950, shows a broaching tool that requires multiple cutting steps and a press to form a set of peripherally spaced broaches. The broaching tool of this patent has no provision for aligning the tool with a work piece.
U.S. Pat. No. 3,722,240 issued to Oliver, Mar. 23, 1973, and Reissue U.S. Pat. No. 30,198, reissued Jan. 29, 1980, disclose lock systems having a shell containing a plurality of pin chambers, each provided with a pin cut at three different levels and at three different angles to provide 3125 different combinations for a five cylinder lock.
U.S. Pat. No. 4,142,391, issued Mar. 6, 1979 to Paig shows a re-keying locking kit that does not include a broach as one of its elements.
U.S. Pat. No. 4,444,033 to Deckert, issued Apr. 24, 1984, shows a pin tumbler lock that is without a broach. Pin bores in one or more plugs are capable of alignment with pin bores in exterior members, so that the plugs may be used with different exterior members.
U.S. Pat. No. 4,635,455, issued Jan. 13, 1987 to Oliver, shows a cylinder lock with twisting tumblers at tumbler positions selectively offset forwardly or rearwardly and selectively rotatable to different angular positions to create an enormous number of keying combinations.
U.S. Pat. No. 4,672,828, issued Jun. 16, 1987 to Theriault, shows a key-in-knob cylinder replacement system that has no broach, only a slot 14 having shoulders 54A and 54B to limit movement of the top 53 of one master pin 15 along slot 14.
U.S. Pat. No. 4,712,401, issued Dec. 15, 1987 to Monahan, shows a re-keyable lock constructed and arranged for inserting and removing master pins of different depth without removing a master pin from the lock. This patent also lacks a broach.
U.S. Pat. No. 4,732,022 issued Mar. 22, 1988 to Oliver, shows a multiple pin tumbler type of lock similar to that shown in U.S. Pat. No. 4,635,455 to Oliver.
U.S. Pat. No. 4,876,783, issued Oct. 31, 1989 and U.S. Pat. No. 5,036,575, issued Aug. 6, 1991, both to Campion et al., show method and apparatus for converting doorknob lock sets to a system utilizing a universal knob and a selected lock cylinder.
U.S. Pat. No. 5,088,996, issued Feb. 12, 1992 to Field, shows a cylinder lock with a changeable keyway. The plug of the lock is reconfigured by inserting conversion parts into its keyway to accept keys of different configuration. This lock also lacks a broach.
U.S. Pat. No. 5,150,996, issued Sep. 29, 1992 to Thoroughman, shows a four-component keyway broach guide assembly that requires access to a broached area from both top and bottom and a machine or press to accomplish broaching. This patent has no guide for aligning a broach, no capability of manual operation and requires shims and friction pieces as part of the patented assembly.
U.S. Pat. No. 5,182,929, issued Feb. 2, 1993 to Myers, shows a method and replacement plug for cylinder locks that converts locks having special keyways requiring correspondingly milled key blanks into a universal keyway lock that can be operated by a multiplicity of differently milled keys.